An airbag assembly is commonly installed in a vehicle to protect an occupant (i.e., a driver or a passenger) in the event of a crash or collision. A typical airbag assembly will comprise an airbag and an inflator. At the onset of a crash or collision, the inflator supplies inflation fluid to the airbag to inflate the airbag into the occupant compartment. An occupant (who is moving forward by inertia) contacts the inflated airbag and is cushioned against impact with a structural part of the vehicle.
In some airbag assemblies, it is desirable to vent the inflated airbag either concurrently with or immediately following the occupant's initial contact with the airbag. Such venting of the inflation fluid permits the airbag to absorb the shock of impact in a gradual manner and provide a softer, less resilient surface for receiving the occupant.
Airbags often include one or more exhaust vents which allow inflation fluid to be "internally vented." In other words, the inflation fluid enters the airbag through an inlet opening and is subsequently vented through exhaust vents into the occupant compartment. However, in an internally vented airbag assembly, the inflation fluid and/or the airbag design must be chosen so that they do not have undesirable effects on an occupant. For example, the inflation fluid must be of a type which is not nauseating or otherwise unacceptable for inhalation by an occupant. Additionally or alternatively, the airbag must be designed so that the venting of the inflation fluid will not raise the pressure in the occupant compartment to an unsafe level or at an unsafe rate.
To overcome the problems commonly associated with internally vented airbag assemblies, airbag assemblies have been developed in which inflation fluid is exhausted to an environment external of the occupant compartment. (See U.S. Pat. No. 3,747,953 to Goes et al.; U.S. Pat. No. 3,778,083 to Hamasaki; U.S. Pat. No. 3,810,523 to Yamaguchi et al.; U.S. Pat. No. 3,861,712 to Matsui et al.; U.S. Pat. No. 4,877,265 to Cuevas; and U.S. Reissue No. 29,228 to Hass.) However, in these airbag assemblies, the inflation fluid enters the airbag through the inlet opening and is subsequently exhausted through the same fluid inlet opening. This "two-way" flow pattern through the airbag inlet opening may create turbulent conditions during the exhausting process.
In some externally vented airbag assemblies, the problems associated with two-way flow have been minimized by the use of valve structures. Such valve structures have likewise been incorporated into internally vented airbag assemblies. However, these valve structures tend to complicate the design, and increase the cost, of the airbag assembly.
Applicant therefore believes that a need remains for an externally vented airbag assembly in which no "two way" flow patterns (and associated problems) are created during the venting process. Additionally, or alternatively, applicant believes a need remains for a valve system which does not complicate the design, or increase the cost, of the airbag assembly.